We wish to purify the genes for the somatic-type 5S RNA from two related amphibians - Xenopus laevis and Xenopus mulleri. The genes for the two-ooycyte type 5S RNA have already been purified. We will compare the structure, redundancy, homogeneity and chromosomal location of the 4 different 5S DNAs. Nucleotide sequence analysis of their spacers will be used to determine initiation, termination and promotor regions. We refer to this as "genetics by evolution". Conservation of sequences within a spacer will be presumed to denote function of spacer regions. The arrangement of sequence and length heterogeneity of repeats within 5S DNA will help to explain how tandem genes evolve. Method for preparing large enough amounts of the 4 kinds of 5S DNA will be developed. This will make possible studies on the proteins which bind to 5S DNA and their arrangement along the tandem repeats. Finally, we hope to isolate 5S DNA in its chromatin form and to reconstruct a molecular environment in vitro in which 5S DNA will be transcribed faithfully by RNA polymerase. BIBLIOGRAPHIC REFERENCES: Brown, Donald D. (1976), Genome organization in higher organisms, Federation Proceedings 35: 1. Brown, Ronald D. and D.D. Brown (1976), The nucleotide sequence adjoining the 3' end of the genes coding for oocyte-type 5S ribosomal RNA in Xenopus, J. Mol. Biol., 102: 1-14.